KepCo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the KepCo Observatory clear sky chart from 2005-11-05 to 2017-04-30.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
38%
14418
12%
45611
9%
14389
43%
14389
17%
31555

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
25%
719
7%
2506
5%
716
28%
716
8%
2003
January16th to endNight
29%
768
8%
2688
7%
768
32%
768
10%
2066
February1st to 15thNight
32%
702
8%
2381
7%
700
35%
700
12%
1778
February16th to endNight
38%
632
13%
1945
8%
632
44%
632
17%
1376
March1st to 15thNight
30%
720
9%
2160
6%
720
34%
720
13%
1641
March16th to endNight
30%
768
9%
2005
4%
768
34%
768
15%
1533
April1st to 15thNight
38%
719
11%
1799
5%
719
41%
719
19%
1328
April16th to endNight
38%
528
14%
1602
9%
528
43%
528
18%
1081
May1st to 15thNight
39%
329
16%
1320
16%
329
48%
329
18%
751
May16th to endNight
40%
342
7%
1368
7%
342
45%
342
14%
887
June1st to 15thNight
41%
330
6%
1173
3%
330
43%
330
19%
742
June16th to endNight
43%
330
8%
1051
1%
330
46%
330
22%
641
July1st to 15thNight
55%
310
11%
1232
8%
310
60%
310
32%
554
July16th to endNight
59%
348
18%
1304
20%
326
74%
326
39%
553
August1st to 15thNight
69%
330
24%
1312
32%
328
75%
328
36%
579
August16th to endNight
61%
598
25%
1648
15%
598
68%
598
42%
873
September1st to 15thNight
61%
660
27%
1650
13%
660
65%
660
45%
924
September16th to endNight
58%
656
25%
1782
16%
656
63%
656
32%
1085
October1st to 15thNight
44%
660
16%
1972
15%
660
48%
660
23%
1279
October16th to endNight
37%
704
12%
2269
8%
704
44%
704
15%
1617
November1st to 15thNight
31%
700
10%
2359
8%
700
35%
700
11%
1825
November16th to endNight
26%
759
7%
2559
5%
759
30%
759
8%
2039
December1st to 15thNight
29%
900
8%
2700
5%
900
31%
900
11%
2116
December16th to endNight
23%
906
9%
2826
3%
906
28%
906
8%
2284

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
12%9%46%5%35%5%5%6%35%
46121
Night
13%10%46%5%3445%6%35%
45778
Cloud CoverDay
11%9%46%6%35%5%5%6%34%
46121
Night
12%10%46%5%3445%6%35%
45782
TransparencyDay
48%6%13%19%9%1
45792
Night
48%6%14%20%9%1
45611
SeeingDay
17%22%24%22%9%2
5180
Night
16%20%15%27%16%3
14423

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%14%6%10%7%34345%21%
1432
16th to endDay
14%16%38%5%33446%28%
1536
February1st to 15thDay
15%16%5%7%5%3445%6%24%
1483
16th to endDay
12%13%48%7%35%5%6%6%26%
1528
March1st to 15thDay
16%15%5%7%5%35%5%5%7%22%
1800
16th to endDay
14%13%6%9%7%45%6%6%7%18%
2218
April1st to 15thDay
10%11%6%11%8%47%5%46%22%
2149
16th to endDay
10%11%48%7%35%5%6%8%28%
2335
May1st to 15thDay
8%9%37%6%46%5%5%7%34%
2301
16th to endDay
14%8%49%7%45%6%6%8%24%
2391
June1st to 15thDay
17%6%36%6%35%5%5%7%30%
2456
16th to endDay
11%8%36%6%36%5%7%6%34%
2569
July1st to 15thDay
44143245%5%7%55%
2313
16th to endDay
431342445%7%59%
2461
August1st to 15thDay
43245%245%5%6%56%
2310
16th to endDay
4323435%46%8%53%
2200
September1st to 15thDay
4414413347%60%
1980
16th to endDay
10%5%2443345%6%48%
1848
October1st to 15thDay
14%6%45%42445%7%40%
1656
16th to endDay
21%12%35%5%235%3430%
1603
November1st to 15thDay
20%12%36%5%35%46%6%24%
1497
16th to endDay
19%11%7%7%4246%5%6%24%
1388
December1st to 15thDay
15%11%6%9%6%35%45%6%25%
1260
16th to endDay
19%18%6%8%5%23335%23%
1407
January1st to 15thNight
21%14%6%8%5%33445%21%
2506
16th to endNight
14%18%5%8%5%34346%23%
2688
February1st to 15thNight
16%14%5%7%5%24446%29%
2369
16th to endNight
11%13%46%425%45%8%32%
1945
March1st to 15thNight
14%11%5%8%5%35%5%6%7%25%
2160
16th to endNight
11%12%48%6%35%5%5%6%28%
2001
April1st to 15thNight
10%9%37%6%37%6%6%7%32%
1799
16th to endNight
6%8%46%6%36%5%5%7%38%
1602
May1st to 15thNight
8%5%26%5%4445%6%46%
1319
16th to endNight
11%6%26%6%37%6%6%8%32%
1368
June1st to 15thNight
13%5%24446%5%5%9%37%
1173
16th to endNight
8%5%235%35%5%6%7%44%
1051
July1st to 15thNight
331322335%7%62%
1312
16th to endNight
1213223447%67%
1400
August1st to 15thNight
221332345%9%62%
1320
16th to endNight
331231436%8%59%
1648
September1st to 15thNight
4313223447%62%
1650
16th to endNight
8%5%24423448%50%
1782
October1st to 15thNight
13%7%34424446%43%
1972
16th to endNight
18%9%37%4345%6%5%31%
2269
November1st to 15thNight
22%12%36%5%34446%24%
2359
16th to endNight
20%14%5%9%5%3443423%
2559
December1st to 15thNight
16%13%5%10%6%24445%25%
2700
16th to endNight
19%20%6%7%5%2333423%
2826

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%16%6%11%6%45%435%20%
1432
16th to endDay
15%15%5%7%5%3446%5%26%
1536
February1st to 15thDay
14%16%6%6%6%35%45%7%23%
1483
16th to endDay
10%13%47%7%35%6%6%6%26%
1528
March1st to 15thDay
15%14%5%7%7%35%6%5%8%21%
1800
16th to endDay
13%13%6%10%8%36%5%6%5%18%
2218
April1st to 15thDay
10%11%6%11%8%5%6%5%5%7%21%
2149
16th to endDay
9%11%5%8%7%45%5%6%8%28%
2335
May1st to 15thDay
9%8%37%7%46%5%5%6%34%
2301
16th to endDay
14%8%48%8%46%5%6%7%23%
2391
June1st to 15thDay
16%7%37%7%45%5%5%6%29%
2456
16th to endDay
11%8%46%6%45%5%5%7%33%
2569
July1st to 15thDay
44234245%5%6%54%
2313
16th to endDay
3323434447%58%
2461
August1st to 15thDay
431442446%6%56%
2310
16th to endDay
4314435%5%6%8%52%
2200
September1st to 15thDay
4424323347%59%
1980
16th to endDay
10%415%5%3445%7%48%
1848
October1st to 15thDay
13%7%35%42445%8%39%
1656
16th to endDay
19%12%36%5%34446%29%
1603
November1st to 15thDay
18%12%46%5%35%5%5%7%24%
1497
16th to endDay
16%14%6%6%6%45%5%5%5%23%
1388
December1st to 15thDay
14%12%5%9%7%35%5%45%26%
1260
16th to endDay
16%19%6%8%5%3444423%
1407
January1st to 15thNight
19%15%6%10%6%3344420%
2506
16th to endNight
14%17%6%10%6%3445%5%21%
2688
February1st to 15thNight
15%14%6%7%5%24446%28%
2369
16th to endNight
10%12%46%5%25%5%5%7%32%
1945
March1st to 15thNight
13%11%46%7%35%6%6%7%26%
2160
16th to endNight
10%12%48%8%46%46%6%27%
2005
April1st to 15thNight
10%7%47%6%46%6%5%7%32%
1799
16th to endNight
6%7%47%6%47%5%5%8%37%
1602
May1st to 15thNight
8%5%246%35%45%6%46%
1319
16th to endNight
10%8%35%6%45%7%6%9%32%
1368
June1st to 15thNight
13%5%25%6%35%5%7%8%37%
1173
16th to endNight
8%5%345%35%5%6%7%43%
1051
July1st to 15thNight
331331345%8%61%
1312
16th to endNight
1112323349%65%
1400
August1st to 15thNight
23332445%8%61%
1320
16th to endNight
231332336%8%60%
1648
September1st to 15thNight
321332346%6%62%
1650
16th to endNight
7%4245%34438%50%
1782
October1st to 15thNight
12%6%36%423446%43%
1972
16th to endNight
17%9%26%5%35%5%5%6%31%
2269
November1st to 15thNight
20%11%47%6%35%45%5%25%
2359
16th to endNight
19%15%5%8%7%3433423%
2559
December1st to 15thNight
16%14%6%9%6%34445%24%
2700
16th to endNight
18%20%6%8%5%2333422%
2826

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
64%6%12%11%4
1432
16th to endDay
55%7%14%15%41
1536
February1st to 15thDay
59%8%17%12%2
1483
16th to endDay
56%8%13%14%7%
1528
March1st to 15thDay
59%8%14%13%3
1800
16th to endDay
63%8%14%10%3
2218
April1st to 15thDay
61%7%13%13%3
2149
16th to endDay
52%8%14%20%41
2335
May1st to 15thDay
47%6%13%22%8%
2301
16th to endDay
56%6%16%14%4
2395
June1st to 15thDay
54%5%11%16%8%2
2456
16th to endDay
48%6%12%21%10%
2569
July1st to 15thDay
29%411%25%21%7%
2164
16th to endDay
25%5%10%26%24%7%
2294
August1st to 15thDay
26%5%11%32%19%3
2293
16th to endDay
27%7%12%29%19%3
2200
September1st to 15thDay
25%413%30%22%3
1980
16th to endDay
34%8%14%26%14%2
1848
October1st to 15thDay
42%7%15%25%8%
1656
16th to endDay
55%6%13%18%5%
1603
November1st to 15thDay
58%8%14%13%31
1497
16th to endDay
59%8%12%15%4
1388
December1st to 15thDay
58%8%13%15%3
1260
16th to endDay
63%6%12%13%3
1407
January1st to 15thNight
65%5%12%10%4
2506
16th to endNight
61%5%13%12%41
2688
February1st to 15thNight
56%7%16%14%41
2381
16th to endNight
49%7%17%19%6%
1945
March1st to 15thNight
54%8%15%16%3
2160
16th to endNight
54%7%15%17%4
2005
April1st to 15thNight
47%8%15%20%6%
1799
16th to endNight
43%7%15%25%6%
1602
May1st to 15thNight
37%5%15%26%14%1
1320
16th to endNight
44%8%21%19%6%
1368
June1st to 15thNight
41%6%14%24%11%1
1173
16th to endNight
36%6%17%24%14%1
1051
July1st to 15thNight
22%412%29%23%7%
1232
16th to endNight
17%412%29%27%8%
1304
August1st to 15thNight
19%5%13%34%23%3
1312
16th to endNight
21%5%13%33%23%2
1648
September1st to 15thNight
20%5%13%30%25%4
1650
16th to endNight
32%6%12%28%16%4
1782
October1st to 15thNight
41%5%16%24%11%1
1972
16th to endNight
51%7%13%22%4
2269
November1st to 15thNight
59%8%12%13%41
2359
16th to endNight
64%5%10%12%5%
2559
December1st to 15thNight
60%6%13%14%3
2700
16th to endNight
66%6%9%13%4
2826

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%6%11%33%23%8%
60
16th to endDay
39%6%17%23%9%4
64
February1st to 15thDay
23%19%25%23%6%
143
16th to endDay
18%20%21%27%9%1
229
March1st to 15thDay
31%31%25%10%1
270
16th to endDay
24%35%20%15%4
288
April1st to 15thDay
21%27%26%15%7%1
269
16th to endDay
17%33%23%15%6%3
267
May1st to 15thDay
17%30%23%21%6%
228
16th to endDay
18%20%25%17%12%4
266
June1st to 15thDay
13%22%22%24%14%2
401
16th to endDay
11%25%23%24%12%2
514
July1st to 15thDay
8%22%25%31%8%3
248
16th to endDay
421%34%24%12%3
271
August1st to 15thDay
9%15%24%34%10%5%
255
16th to endDay
8%21%29%29%7%4
268
September1st to 15thDay
7%23%24%25%15%3
255
16th to endDay
15%19%27%23%10%3
255
October1st to 15thDay
23%20%27%19%7%1
255
16th to endDay
40%8%18%20%11%1
115
November1st to 15thDay
30%12%25%26%5%
75
16th to endDay
25%13%23%10%18%10%
60
December1st to 15thDay
26%6%25%25%13%3
60
16th to endDay
26%7%25%23%12%4
64
January1st to 15thNight
22%23%14%25%11%2
720
16th to endNight
19%20%16%27%14%1
768
February1st to 15thNight
19%21%14%25%15%2
704
16th to endNight
16%20%16%27%16%3
632
March1st to 15thNight
19%24%18%24%11%1
720
16th to endNight
16%24%20%24%11%1
768
April1st to 15thNight
11%22%17%26%17%4
719
16th to endNight
9%24%19%29%14%3
528
May1st to 15thNight
10%26%16%27%16%2
330
16th to endNight
13%22%13%25%20%4
343
June1st to 15thNight
10%23%16%26%20%2
330
16th to endNight
11%21%15%28%20%2
330
July1st to 15thNight
6%19%14%26%29%5%
310
16th to endNight
222%10%31%29%3
348
August1st to 15thNight
313%10%26%40%6%
330
16th to endNight
414%14%33%27%5%
598
September1st to 15thNight
5%14%15%26%26%12%
660
16th to endNight
11%12%11%32%26%5%
656
October1st to 15thNight
18%14%16%26%21%2
660
16th to endNight
23%12%16%27%16%3
704
November1st to 15thNight
23%22%15%29%8%1
700
16th to endNight
25%24%12%21%12%3
759
December1st to 15thNight
21%23%15%30%8%1
900
16th to endNight
26%22%18%26%6%
906
Page generated at 2017-04-30 17:39:59. Version ac04

Copyright 2017 A. Danko


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